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Fork travel

Discussion in 'The Garage' started by yellowdog, Apr 23, 2015.

  1. When pushing down on the front end and then letting the forks come back up they are coming back up with a thump as they reach the end of their travel,it is a distinct clonk and it happens when going over a bump in the road as well ,any thoughts please as to what is happening .Thanks
  2. chizler62

    chizler62 XS650 Addict

    1st raise front wheel off ground. Grab wheel with one hand and brace yourself against frame someway and jiggle wheel back and forth same axis as riding. Wheel bearing? Lower tubes loose on uppers? Steering head bearings? Etc

    2nd I'd loosen everything, axle, axle pinch bolts, fork brace - basically everything under the fork seals. Find anything already loose?

    Compress several times with everything slightly loose. Then tighten everything properly. Check again.

    There are known issues inside the forks. But, those are first steps before ripping apart the forks. IMO

    Posted via Mobile
  3. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    I'll vote mis-assembled, rebound spring not in the correct place? What year forks?
  4. Thanks ,all original 72 forks ,thought it might be not enough oil or weak springs.
  5. 5twins

    5twins XS650 Guru Top Contributor

    It sounds like the forks are topping out. Later forks have a small top out spring to stop the clunking at full fork extension. I don't think the earlier ones have this. I think it started with the '78 forks. I did add the springs to a set of '77 forks I refurbed but I'm not sure this is something you could do. What you're experiencing may be normal but I can't say for sure. I've never had any of the early forks around to deal with.
  6. XSLeo

    XSLeo XS650 Guru Top Contributor

    Oil is easy to fix, drain out the old, flush with Kerosene or what ever cleaner you like. drain out and let drain over night.
    Now with the top caps off the forks, springs out, compress forks. add about 8 ounces of oil. This is too much but soon to be right.
    Take a few feet of clear hose, Put a zip tie 6 inches from one end. Put this six inch end down into the forks. I use a Miti Vac tool hooked to this hose to draw out the oil above the end of the hose. You can use any method to apply vacuum to the hose, even by mouth. Not to tasty but works.
    This is the 6 inch down method of fork oil setting. This improves fork action by giving a bit of an air shock effect. This helps reduce brake dive, as well as firmer action.
    Now extend the forks install the springs and caps, or new springs.
    You can experiment with different oil weights to see which feels best to you.
    One more thing, before replacing the springs you can try adding spacers for the springs. I'm not sure just how your forks are set up. My 75 has a steel spacer on top of the spring. You can make spacers from PVC pipe. Cut a set 1/2 longer than the spacer you have. A set at 3/4 inch longer. Maybe even an inch longer. Try each length of spacer. You may find that works. Just don't go too far, don't want to get spring bind. This is when a spring compresses till the turns touch. This make the spring just a steel tube. Ride gets rough.
    Last edited: Apr 24, 2015
  7. Thanks again ,I will give this a bash tomorrow.
  8. grizld1

    grizld1 Grumpy old man Top Contributor

    5twins is correct: there were no top out springs installed prior to 78, and your 72 forks are going to do what they're doing no matter what you try, short of trying to mod the forks with top out springs or finding smoother roads. The clunk is normal for pre-78 models, and changing oil viscosity, etc. will not eliminate it, although heavier oil will definitely aggravate the inherent vices of a damper rod fork that's already undersprung and overdamped. BTW, heavier springs will only make the rebound contact harder.
  9. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    OK The diagram I looked at also indicated no top out springs. On the other hand I have been riding my 73 on the local beat up frost heaved Wisconsin back roads and haven't been getting any clunking. So I went down stairs grabbed the 73 front brake and repeatedly jerked up and back on the bars hard enough to slide the front tire back. Result? No clunking. There were some changes in the fork 72 73. This is just a stock fork with slightly leaky fork seals on a bike with 15K miles. I'll repeat the experiment on a drum front bike or two tomorrow and maybe even some 72 forks I have on the shelf and one set on a bike with 6 over tubes (roll eyes). But what I am thinking is that your early fork SHOULDN'T clunk hard and loud like that. I'll go back to; internally somethings not right.

    Oh I have had fork clunking on bikes with loose steering bearings, especially the tapered bearings.
    Last edited: Apr 24, 2015
  10. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    One more thing; The 72 has a one year only oddball disk brake mount. It depends on rubber pads between the rotor and wheel to transmit forces. If the pads are hammered flat or MIA the brake rotor will clunk back and forth as the rotor tangs hammer the wheel hub slots..... The parts count on that brake is sky high, mis-assembly is easy, no surprise it was a one year wonder. Yamaha had a service bulletin with new parts that eliminated the rubber pads. Theres an old thread around here somewhere with that info.
  11. Drained the old oil today and barely any came out ,refilled with 10/30 castrol fork oil,tried the 6" tube method but not sure if I got it right ,any way it seems a bit better now only a light clunk now which is possibly coming from the handle bars .
    Interesting about the head races though ,I bought the tapered bearings from All Balls and when I fitted them they did seem to go in quite easily and then some time later I saw something on here about the 72 neck being a slightly different size to the other models ie a little bigger, can't find that info now so does this sound right ?
  12. Two many ,yes that's sounds the same as mine,by the sound of it it's not critical so is probably not the cause of my "clunk"
  13. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Just to be sure, double-checked the 70-73 parts manuals, and the steering races remained the same for those years...
  14. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    I went and tried several as they sit early bike forks 70 to 73. All but one were reluctant to clunk at all. The one 70 would clunk a bit with an enthusiastic tug upwards with the brakes on. It FEELS like there is a hydraulic cushion stopping that last bit of travel, so very low fork oil may affect the top out damping. Understand it was not as cushy as the spring damped stop on the newer bikes. One thing that comes to mind is that stiffer springs or an added spacer would reduce static sag and may increase an end of travel clunk. I did not have any bare necks to measure the top bearing bore ID, maybe later in the week.

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